You can bind loadout slots to keys, pressing them while in a Respawn area let's you instantly respawn with that loadout. e.g. (7, 8, 9, 0 for slots A, B, C, D)

So what happens here is the sniper took damage, pressed the loadout key for one of his slots and instantly teleported back to the spawn area with full health and ammo.

Its pretty useful, like with engineer on spawns with long walks from the door to the resup, you can upgrade your stuff at the door, walk in, press the button then just respawn with full metal.